Field of the Invention
The present invention relates to wireless communication, and more particularly, to a method for operating a user equipment (UE) for supporting interworking between heterogeneous networks in a wireless communication system and the user equipment using the same.
Related Art
3GPP (3rd Generation Partnership Project) LTE (long term evolution), a development of UMTS (Universal Mobile Telecommunication System), was introduced in 3GPP Release 8. 3GPP LTE uses OFDMA (orthogonal frequency division multiple access) for the downlink and SC-FDMA (Single Carrier-frequency division multiple access for the uplink. Recently, there have been discussions about 3GPP LTE-A (LTE-Advanced), which is an evolution of 3GPP LTE.
A wireless communication system may have support for services to UEs over multiple access networks. For example, a UE may receive service from a 3GPP access network, which is a wireless communication system, and also may receive service from a non-3GPP access network, such as WIMAX (Worldwide Interoperability for Microwave Access) or WLAN (Wireless Local Area Network).
A UE may establish a connection with a 3GPP access network to receive a service, and if traffic overload occurs to the 3GPP access network, may handle the traffic over another access network, i.e., a non-3GPP access network, to improve the overall network efficiency. Reversely, a UE connected to a non-3GPP access network may handle traffic using a 3GPP access network for efficiency.
Suppose that there are two different networks: a first network and a second network. Interworking refers to the ability of a UE connected to the first network to access and use resources or services offered by the second network. In the conventional art, the UE is given predetermined rules for interworking and performs interworking according to these rules. That is, a network informs the UE of interworking rules, and the UE performs interworking by itself.
Meanwhile, a transmitting end may split one data stream into multiple partial streams and transmit them over different networks, and a receiving end may receive and aggregate the multiple partial streams into a data stream. For example, the transmitting end may split a data stream into first and second partial streams, and transmit the first partial stream over a 3GPP access network (e.g., LTE) and the second partial stream over a non-3GPP access network (e.g., WLAN). Then, the receiving end may receive the first and second partial streams over the LTE and the WLAN and aggregate them to restore/create the single data stream.
In this transmission scheme, it is very important to control transmission delays to below a certain value when transmitting each partial stream. If the transmission delay of a particular partial stream is greater than the certain value, it is hard to aggregate the partial streams in sequence into the original data stream, and re-transmissions of the partial streams may occur, thus leading to an abrupt decrease in transmission efficiency.
By the way, in the conventional art, it is not a network but a UE that determines whether to perform interworking or not, which makes it difficult for the network to control transmission efficiency. For example, in some situations, a UE connected to a first network may interwork with a second AP, among APs (access points) in a second network, while there are difficulties in interworking with a first AP. According to the conventional art, it is hard for the first network to control the UE since it cannot be aware of the situation.